Abstract
The chlorophyll dimer P680 traps the light energy and its redox potential (E'0 > +1.2 V) fixes the driving force available for water oxidation. In this study, to know the effect of a ligand of D1 side of P680 (PD1) to its redox potential in PSII, we analyzed PSII from the thermophilic cyanobacterium Thermosynechococcus elongatus in which a normal His ligand of PD1 was substituted for either Ala or Gln by site-directed mutagenesis.
Both mutant cells grew photo-autotrophically. However, the amounts of phycobilliproteins in the mutants were smaller than in the WT*. The energy transfer from phycocyanin to PSII via allophycocyanin in both mutants was not efficient as that in WT*. Purified PSII core complexes were fully active in oxygen-evolution. FTIR spectra shows the stractural changes of P680. Flash-induced absorption changes and themperature shifts in themoluminescence spectra suggested possible changes in the redox potential of P680 +/ P680.
